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Residue Treatment

Reusing Most of the Materials

Thermal waste treatment produces residues which can be either reused or landfilled. The principal components are slags and ashes, consisting mostly of non-combustible waste constituents such as glass, minerals or scrap metals. Flue gas cleaning also forms reaction products. The volume and nature of the residues produced depend mainly on the composition of the waste and the process used in the particular treatment concept. With an intelligent secondary treatment process, large parts of these materials can often be reused.

InovaRe

InovaRe by HZI – Efficient Material Recovery from Waste

Recovering metals from bottom ash is an aspect of urban mining that is becoming increasingly significant for the operators of EfW plants. As well as enabling valuable commodities such as copper and aluminum to be recycled profitably from the bottom ash, it also saves huge amounts of CO2. For example, recycling aluminum from bottom ash requires just 10% of the energy required for primary production.

In addition to the tried-and-tested wet discharge process, HZI also offers InovaRe: a modular complete solution for the efficient recovery of materials from bottom ash. Developed in-house, it is suitable for both wet and dry discharge.

Dry mechanical bottom ash treatment

This widely used technology is suitable for use with wet or dry discharge of bottom ash, recovering metals and mineral materials that can be recycled as secondary raw materials and for use in construction.

Most commonly used technology, with many years’ operational experience

Low investment costs

Environmental benefits through avoidance of process water

Grate for Riddlings

Most plant operators recover valuable materials such as copper and aluminum from the bottom ash. These are mainly fractions in the >10mm range. However, the most valuable metal particles are to be found in the <10mm fine fraction. The latter makes up some 40% of the total bottom ash, but recovering metals from wet discharge is only possible to a very limited extent.
HZI’s Grate for Riddlings (GfR) addresses this problem. GfR modification final grate zone that allows particles be extracted directly and discharged in dry form.

High metal recovery rate and above-average quality of discharged metals

Higher overall plant profitability thanks to profitable recycling

Recycling of recovered materials improves CO2 footprint

HZI DryMining is an ideal supplement to the Grate for Riddlings for treating extracted bottom ash.

HZI DryMining

The dry mining tower for fine bottom ash treatment has a maximum capacity of 10 t/h. HZI DryMining is ideal for individual plants that have no suitable metal recovery installation nearby and for groups of plants that want to share the investment costs. An alternative business model is to use it as a bottom ash treatment facility in its own right.

The discharged bottom ash is fractioned and treated in several phases, with separation of different metals in different densities. This ensures the recovered metals are of high quality.

Fully automated system

Non-ferrous metals can be recycled directly

Improved CO2 footprint

HZI DryMining enhances plant profitability, either in combination with the Grate for Riddlings or as a stand-alone solution.

Fly Ash Washing

If fly ash is collected separately from bottom ash and flue gas cleaning residues, two different methods may be applied to remove or immobilize fly ash contaminants:

Acid washing of fly ash using acidic scrubber blowdown removes heavy metals in a recyclable form and produces a fly ash which can be disposed with the bottom ash.

Neutral washing followed by solidification by adding binders to condition the fly ash into a leach resistant matrix

Acidic Fly Ash Washing

This process is an ideal combination of two flue gas cleaning residues: Acidic fly ash washing uses acidic scrubber blowdown to wash out the heavy metals from fly ash. Heavy metals can be recovered in the effluent treatment stage and recycled.

Neutral Fly Ash Washing

The aim of this process is to transform fly ash into a stable, leach proof matrix. Neutral, easily soluble salts are extracted in a cascade of stirred vessels. By controlling pH in a slightly alkaline range, soluble heavy metals are precipitated. Washing liquid is separated from the solids by filtration and cleaned in the effluent treatment stage. Dewatered solids are mixed with hydraulic binders to form a solid, stable and leach resistant matrix when landfilled.

Effluent Treatment

Capture and Recycle Contaminants

The effluent treatment process neutralizes blowdown from wet flue gas scrubbers or from fly ash washing and removes contaminants such as heavy metals, ammonia or persistent organic pollutants (POPs). Depending on the plant configuration, some contaminants such as mercury or zinc can be recovered for recycling. The only remaining components in the cleaned effluent are naturally occurring salts such as sodium and calcium chlorides and sulfates.

Set the pH

Often lime slurry is used to neutralize acidic scrubber effluents. In a first step the pH is controlled to transform dissolved heavy metals into less soluble complexes. Induced flocculation enhances the precipitation of fine particulates, gypsum and metal complexes which allows separation in a sedimentation tank or a filter. Thereafter the pH is adjusted to the neutral range and a second purification is carried out with specific ion exchangers and activated carbon beds. After a final quality control, the clean effluent is discharged. The precipitated sludge is dewatered in a filtration system for final disposal.

Technology

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